I've done the 3 main ones, the class ones and one heroic. The heroic ones are insane. Opoonents have 45hp. First guy's power now summons 4/4's, and some his cards are better. The second one's power now costs 1mana and those acolytes are now 3/4's and give 3 attack to the hero. The third one has a 0 mana, return two minions to your opponent's hand, and starts with 2 haunted spiders. Second boss still easy is beaten by zoolock. The first one I'm told fell to Handlock, and the third I think will be weakest agaisnt Freeze mage.
Also, my impressions of the new cards are that Egg is the most useful. Haunted spider I can see maybe putting in an aggro paladin deck, but I don't think it's very valuable. The Battlecries cost more one seems fairly weak. I mean, what are you trying to counter with it? Chances are you have battlecry minions too, because they are some of the best ones (argus, SSC, Fire Elemental). Maexanna seems ok, but at 6 mana it better be killing Yetis and Drakes. If it's killing anything with 8 attack then it's no better than Cobra. I guess if you can buff it I guess it's great. Haven't tried it out yet though.